1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method of fabricating an LCD device, and more particularly, to a reflection-type LCD device and a method of fabricating a reflection-type LCD device.
2. Discussion of the Related Art
As demand for various display devices increases, efforts have been made to develop liquid crystal display (LCD) devices, plasma display panel (PDP) devices, electroluminescent display (ELD) devices, and vacuum fluorescent display (VFD) devices. Among these various flat display devices, the LCD devices have been commonly used as substitutes for cathode ray tube (CRT) devices due to their thin profiles, light weight, and low power consumption. In addition to mobile-type LCD devices, such as displays for notebook computers, the LCD devices have been developed for use in computer monitors and televisions to receive and display broadcasting signals.
Despite various technical developments within the LCD device technology, improved image quality of the LCD devices has been lacking. Accordingly, in order to use the LCD devices as general displays, providing images having high resolution and high luminance with a large-sized screen must be attained while still maintaining their thin profile, light weight, and low power consumption.
In general, an LCD device includes an LCD panel for displaying images and a driving part for supplying driving signals to the LCD panel. In addition, the LCD panel includes first and second glass substrates bonded to each other at a predetermined interval with a liquid crystal layer injected between the first and second glass substrates. The first glass substrate (i.e., TFT array substrate) includes a plurality of gate and data lines, a plurality of pixel electrodes, and a plurality of thin film transistors. The plurality of gate lines are formed along a first direction at fixed intervals, and the plurality of data lines are formed along a second direction perpendicular to the gate lines at fixed intervals, thereby defining a plurality of pixel regions. Accordingly, the plurality of pixel electrodes are formed within the pixel regions in a matrix configuration, and the plurality of thin film transistors are switched according to signals provided to the gate lines so as to supply signals of the data lines to the respective pixel electrodes.
The second glass substrate (i.e., color filter substrate) includes a black matrix layer for shielding portions of the first glass substrate, except for the pixel regions, from light. In addition, a red (R), green (G), and blue (B) color filter layer is provided for displaying various light colors, and a common electrode is used for producing an image.
The LCD device is driven according to optical anisotropy and polarizing characteristics of liquid crystal material. The liquid crystal material includes liquid crystal molecules, wherein each liquid crystal molecule has a long and thin structure to control an alignment direction of the liquid crystal molecules by inducing an electric field to the liquid crystal material. By controlling the alignment direction of the liquid crystal molecules, light passing through the liquid crystal material is refracted according to the alignment direction of the liquid crystal molecules by the optical anisotropy of the liquid crystal material, thereby displaying images.
The LCD device is commonly classified into transmission type LCD devices that display images by using an additional light source, such as a backlight, and reflection-type LCD devices that display images by making use of ambient light. The reflection-type LCD devices have advantageous operational characteristics that result in low power consumption, thereby producing high quality images in an outdoor environment. In addition, the reflection-type LCD devices have thin profiles and light weight since they do not require an additional light source, such as the backlight.
However, the present reflection-type LCD devices may not be able to effectively cope with the demands for high resolution and improved color realization ratios since their display screens are displayed in a dark state. That is, the current reflection-type LCD devices are commonly used for displaying limited types of images, such as numbers and simple characters. Accordingly, in order to incorporate the reflection-type LCD device in various display devices, it is necessary to improve reflectivity, resolution, and color realization ratios. In addition, the reflection-type LCD devices need to obtain rapid response times and high contrast ratios.
The current reflection-type LCD devices have been developed with improved reflectivity of a reflective electrode, and have a super aperture technology. For example, U.S. Pat. No. 5,610,741 discloses a reflection-type LCD device that improves reflectivity by forming minute bumps on the reflective electrode, and is hereby incorporated by reference.
FIG. 1 is a plan view of a reflection type LCD device according to the related art, and FIG. 2 is a cross sectional view along I-I′ of FIG. 1 according to the related art. In FIG. 1, the reflection-type LCD device includes a lower substrate 10 (in FIG. 2) having gate and data lines 11 and 12 crossing each other, a pixel electrode 13, and a thin film transistor that includes a gate electrode 11a, a semiconductor layer 14, and source/drain electrodes 12a and 12b formed at a crossing point of the gate and data lines 11 and 12. Accordingly, the gate and data lines 11 and 12 define a pixel region by crossing each other, and the pixel electrode 13 is formed within the pixel region. In FIG. 1, the thin film transistor functions as a switching device, wherein the thin film transistor operates to supply data signals to a reflective electrode 13 by switching signals supplied to the gate electrode 11a. In addition, the reflective electrode 13 is formed of an opaque metal material having great reflectivity, such as Al or Ag, so as to reflect the light incident through an upper substrate 20 (in FIG. 2).
In FIG. 2, the gate line 11 is formed on the lower substrate 10 to extend along a first direction, wherein the gate electrode 11a protrudes from the gate line 11. Then, a gate insulating layer 15 is formed along an entire surface of the lower substrate 10 including the gate electrode 11a. Next, the island-shaped semiconductor layer 14 is formed on the gate insulating layer 15 to overlap the gate electrode 11a. Then, the data line 12 is formed to extend along a second direction perpendicular to the gate line 11, wherein the source/drain electrodes 12a and 12b are formed to overlap both sides of the semiconductor layer 14. Accordingly, the source electrode 12a protrudes from the data line 12, and the drain electrode 12b is formed at a predetermined interval from the source electrode 12a. 
Next, a passivation layer 16 is formed along an entire surface of the lower substrate 10 including the source/drain electrodes 12a and 12b, and is selectively removed, thereby forming a contact hole exposing a portion of the drain electrode 12b. Then, a reflective metal layer is deposited thereon, and patterned so as to form the reflective electrode 13 within the pixel region, and is formed to be electrically connected with the drain electrode 12b. Accordingly, the reflective electrode 13 functions to reflect any external light and serves as the pixel electrode of receiving the data signals from the drain electrode 12b. 
Next, the upper substrate 20 includes a black matrix layer 21 for shielding portions of the lower substrate 10, except for the pixel regions, from the light and a color filter layer 22 for producing colored light within the pixel regions. The color filter layer 22 is formed of a photosensitive resin that absorbs light. Then, a common electrode 23 is formed along an entire surface of the upper substrate 20 including the color filter layer 22.
Next, a light-diffusion plate 24 is formed at a rear portion of the upper substrate 20. Thus, a reflective function of the reflective electrode 13 is strengthened by the light-diffusion plate 24, thereby improving light efficiency. However, it is difficult to improve the luminance of the LCD device using the light reflected and emitted by the reflective electrode 13. Accordingly, the light-diffusion plate 24 is additionally formed on the upper substrate 20 to obtain high luminance by making use of the light-diffusion characteristics of the light-diffusion plate 24.
Next, ball spacers (not shown) are spread onto the lower and upper substrates 10 and 20. Then, the lower and upper substrates 10 and 20 are bonded to each other, and a liquid crystal layer 30 is formed between the lower and upper substrates 10 and 20.
However, the reflection-type LCD device requires the additional light-diffusion plate 24, thereby making it impossible to obtain an ultra-thin LCD device and decreasing manufacturing costs. In order to overcome these problems, a reflection-type LCD device has been developed that includes grooves in the reflective electrode without using the light-diffusion plate, thereby improving light efficiency of the LCD device.
FIG. 3 is a plan view of another reflection-type LCD device according to the related art, and FIG. 4 is a cross sectional view along II-II′ of FIG. 3 according to the related art. In FIGS. 3 and 4, a reflection-type LCD device includes a lower substrate 10 having gate and data lines 11 and 12, a reflective electrode 13, and a thin film transistor, wherein the gate and data lines 11 and 12 are formed perpendicular to each other to define a pixel region. The reflective electrode 13 is formed within the pixel region, and the thin film transistor includes a gate electrode 11a, a semiconductor layer 14, and source/drain electrodes 12a and 12b formed at a crossing point of the gate and data lines 11 and 12. In addition, a plurality of grooves 18 are formed in a surface of the reflective electrode 13 to reflect any external light. However, improving the luminance is problematic since the number of the grooves formed in one reflective electrode is limited.
Accordingly, the reflection-type LCD device has the following disadvantages. First, the reflection-type LCD device makes use of external light having low luminance, wherein a light-diffusion plate or a plurality of grooves in the surface of the reflective electrode are required, thereby increasing the incident surface and transmission area of the light. Second, when using the light-diffusion plate or the reflective electrode having the grooves, it is impossible to form a ultra-thin LCD device and manufacturing processing steps are complicated. Third, since the color filter layer absorbs the light, the luminance is lowered due to the low light efficiency.